Apparatuses and methods for providing reference voltages

Abstract

A reference voltage generator is disclosed that may provide a plurality of reference voltages. A reference voltage generator may include a voltage divider, a multiplexer coupled to the voltage divider, an operational amplifier that may receive a voltage from the multiplexer, and a plurality of resistors that may receive an output from the operational amplifier. The reference voltages may be provided from output terminals coupled to the resistors. A reference voltage generator may include a voltage divider, two multiplexers coupled to the voltage divider, an operational amplifier coupled to each multiplexer, and a plurality of resistors coupled between the outputs of the two operational amplifiers. Reference voltages may be provided from output terminals coupled to the resistors.

What is claimed is: 
     
       1. An apparatus comprising:
 a multiplexer configured to receive a plurality of voltages and provide a selected voltage; 
 an operational amplifier configured to receive the selected voltage at a first input of the operational amplifier and provide a first reference voltage from an output of the operational amplifier; 
 a resistor coupled to the output of the operational amplifier and a second input of the operational amplifier at a reference node, wherein a second reference voltage is provided at the first reference node; 
 an adjustable resistor having a first terminal coupled to the second input of the operational amplifier and a second terminal coupled to a second reference node, the adjustable resistor configured to adjust a resistance value between the output of the operational amplifier and the second reference node to maintain a voltage between the first reference voltage and the second reference voltage that is constant and independent of a change of the first reference voltage. 
 
     
     
       2. The apparatus of  claim 1  further comprising a plurality of resistors coupled in series between the resistor and the first reference node, wherein additional reference voltages are provided from between adjacent ones of the plurality of resistors. 
     
     
       3. The apparatus of  claim 2  further comprising a capacitor coupled to each respective node between the adjacent ones of the plurality of resistors. 
     
     
       4. The apparatus of  claim 1  further comprising a capacitor coupled to the output of the operational amplifier. 
     
     
       5. An apparatus comprising:
 a multiplexer configured to receive a plurality of voltages and provide a selected voltage; 
 an operational amplifier configured to receive the selected voltage at a first input of the operational amplifier and provide a first reference voltage from an output of the operational amplifier; 
 a resistor coupled to the output of the operational amplifier and a second input of the operational amplifier at a reference node, wherein a second reference voltage is provided at the reference node; and 
 an adjustable resistor coupled to the second input of the operational amplifier, the adjustable resistor configured to maintain a constant voltage between the first reference voltage and the second reference voltage, 
 wherein the operational amplifier is a Class AB operational amplifier. 
 
     
     
       6. An apparatus comprising:
 a multiplexer configured to receive a plurality of voltages and provide a selected voltage; 
 an operational amplifier configured to receive the selected voltage at a first input of the operational amplifier and provide a first reference voltage from an output of the operational amplifier; 
 a resistor coupled to the output of the operational amplifier and a second input of the operational amplifier at a reference node, wherein a second reference voltage is provided at the reference node; 
 an adjustable resistor coupled to the second input of the operational amplifier, the adjustable resistor configured to maintain a constant voltage between the first reference voltage and the second reference voltage; and 
 a second resistor and a capacitor coupled in series between the output of the operational amplifier and a negative voltage supply. 
 
     
     
       7. A method comprising:
 providing a selected voltage to a first input of an operational amplifier and outputting a first reference voltage at an output of the operational amplifier; 
 dividing with a plurality of first resistors the first reference voltage to provide a plurality of reference voltages at a same time at respective nodes between adjacent ones of the plurality of first resistors; 
 providing an output of the one of the plurality of first resistors as feedback to a second input of the operational amplifier; and 
 maintaining, by an adjustable resistor coupled to the plurality of first resistors, a respective voltage between adjacent ones of the plurality of reference voltages that is constant and independent of a change of voltage level of the first reference voltage. 
 
     
     
       8. The method of  claim 7  further comprising:
 dividing a source voltage to provide a plurality of voltages; and 
 selecting the selected voltage from the plurality of voltages. 
 
     
     
       9. The method of  claim 8 , wherein selecting the selected voltage comprises controlling a multiplexer to select the selected voltage from the plurality of voltages. 
     
     
       10. The method of  claim 7 , wherein maintaining the constant voltage includes adjusting the adjustable resistor. 
     
     
       11. The method of  claim 7 , wherein the operational amplifier is a Class AB operational amplifier. 
     
     
       12. The method of  claim 7 , further comprising providing a capacitor coupled to the output of the operational amplifier. 
     
     
       13. The method of  claim 7  further comprising providing a capacitor coupled to each respective node between adjacent ones of a plurality of resistors in series in the first resistor. 
     
     
       14. The method of  claim 7  further comprising providing a second resistor and a capacitor coupled in series between the output of the operational amplifier and a negative voltage supply. 
     
     
       15. The method of  claim 7 , wherein the adjustable resistor is a trimmed resistor. 
     
     
       16. An apparatus comprising:
 a multiplexer configured to receive a plurality of voltages and provide a selected voltage; 
 an operational amplifier configured to receive the selected voltage at a first input of the operational amplifier and provide a first reference voltage from an output of the operational amplifier; 
 a resistor coupled to the output of the operational amplifier; 
 a first adjustable resistor coupled to the resistor and a second input of the operational amplifier at a reference node, wherein a second reference voltage is provided from between the resistor and the first adjustable resistor; and 
 a second adjustable resistor having a first terminal coupled to the second input of the operational amplifier and a second terminal coupled to a node, the second adjustable resistor configured to adjust a resistance value between the output of the operational amplifier and the node to maintain a voltage between the first reference voltage and the second reference voltage that is constant and independent of a change of the first reference voltage. 
 
     
     
       17. The apparatus of  claim 16  further comprising a plurality of resistors coupled in series between the resistor and the first adjustable resistor, wherein additional reference voltages are provided from between adjacent ones of the plurality of resistors. 
     
     
       18. The apparatus of  claim 17  further comprising a capacitor coupled to each respective node between the adjacent ones of the plurality of resistors. 
     
     
       19. The apparatus of  claim 16 , wherein the operational amplifier is a Class AB operational amplifier. 
     
     
       20. The apparatus of  claim 16  further comprising a capacitor coupled to the output of the operational amplifier. 
     
     
       21. The apparatus of  claim 16  further comprising a second resistor and a capacitor coupled in series between the output of the operational amplifier and a negative voltage supply.